1. Field of the Invention
Embodiments relate to a gamma reference voltage generation circuit and a flat panel display using the same.
2. Discussion of the Related Art
Various flat panel displays, whose weight and size are smaller than weight and size of cathode ray tubes, have been recently developed. Examples of the flat panel displays include a liquid crystal display (LCD), a plasma display panel (PDP), a field emission display (FED), and an organic light emitting diode (OLED) display. These flat panel displays have been put to practical use and have been selling.
The liquid crystal display and the OLED display each include a display panel displaying an image in response to driving voltages and driving circuits supplying the driving voltages to the display panel. A plurality of pixels are arranged on the display panel in a matrix format. The plurality of pixels each include an active switching element. In the liquid crystal display, a gray level is represented by controlling a light transmittance of a liquid crystal layer included in the display panel depending on a magnitude of the driving voltage applied to the display panel. In the OLED display, a gray level is represented by controlling an amount of current flowing in an organic light emitting diode depending on a magnitude of the driving voltage applied to the display panel.
Generally, a gray scale may mean that an amount of light that he or she perceives through his or her eye is divided in stages. According to Weber's law, human eye nonlinearly acts on brightness of light. Therefore, if he or she linearly measures changes in brightness of light through his or her eye within a limited bit depth such as k-bit per channel, he or she perceives the brightness of light intermittently change when an amount of light changes. Namely, posterization occurs. Accordingly, the brightness of light needs to be nonlinearly decoded so as to achieve the optimum image quality within a limited bit depth. For this, a difference between driving characteristics of the display panel and characteristics perceived through human eye must be removed. The removing process is called a gamma correction. Generally, a gamma correction method includes setting a plurality of gamma reference voltages fixed depending on the driving characteristics of the display panel, dividing each of the set gamma reference voltages, and compensating gamma values of digital video data.
FIG. 1 shows a gamma correction circuit of a related art flat panel display.
As shown in FIG. 1, a related art gamma correction circuit includes a plurality of digital-to-analog converters (DACs) DAC#k, DAC#k-1, DAC#k-2 . . . respectively generating gamma reference voltages VRG_k, VRG_k-1, VRG_k-2 . . . corresponding to gamma data GMA_Data received from the outside and a resistance string R-String generating a plurality of gamma voltages using the gamma reference voltages VRG_k, VRG_k-1, VRG_k-2 . . . being tap voltages. The DACs DAC#k, DAC#k-1, DAC#k-2 . . . are electrically separated from one another to respectively supply the gamma reference voltages VRG_k, VRG_k-1, VRG_k-2 . . . to tap terminals inside the resistance string R-String. The resistance string R-String divides each of the gamma reference voltages VRG_k, VRG_k-1, VRG_k-2 . . . to generate a plurality of gamma voltages.
On the other hand, the related art flat panel display has the following problems.
Firstly, because the DACs generate the gamma reference voltages independently of one another, the gamma reference voltage inside the resistance string generated by one DAC of the DACs is fixed irrespective of changes in the gamma reference voltage generated by the DAC next to the one DAC. Therefore, when a corresponding gamma reference voltage having a predetermined range needs to change so that an output luminance and a color coordinate are corrected, all the gamma reference voltages other than the corresponding gamma reference voltage have to be individually controlled so as to accord the output luminance characteristics with a desired gamma curve through gamma correction. Namely, the gamma correction causes so much trouble.
Secondly, because a gamma characteristic of the related art flat panel display is determined by a gamma curve of approximately 1.8 to 2.2, a difference between low gray levels are unclear. Namely, a capability to represent a low gray level falls.